Power-up by plate

Ship & Boat International: eNews January/February 2018

For hybrid- and all-electric ferries, ‘refuelling’ at port-based, electric recharging points can sometimes prove more challenging in practice than in theory. For instance, this process often necessitates a significant amount of cabling and plug-in connections, spread out across the berth or dock, to top up the ferry’s energy storage – all of which equipment is continually subject to physical wear and the effects of a sea-facing environment.

Drawing on his own experience of the recharging process with plug-connected systems, Ingve Sørfonn, technology manager for electrical and automation power conversion at Wärtsilä, recalls occasions on which plugs and cables have been damaged. He tells Ship & Boat International: “If you have plug-in connections to the extent of 15,000 to 20,000 connections each year, there’ll obviously be a need for maintenance and replacement of parts – not only of the plug itself, but also of all other movable parts.” Just one damaged component can hinder attempts to refuel an electric ferry, leading to potential service disruption and loss of revenue and reputation.

Add airborne salinity, harsh rainfall, winter frosts and rough handling by port-based personnel to the mix, and the cost of maintaining all components and replacing damaged parts soon adds up.

To this end, and partly inspired by developments in the automotive and smartphone/mobile industries, Wärtsilä has produced an automatic wireless induction charging system, intended to dispense with plugs and cable connections during the vessel recharging process. The first (and, to date, only) application of this innovative system has been aboard Norled’s double-ended, 85m x 15.5m ferry Folgefonn.

Built by Trondheim Verft, Norway in 1998, the 300-passenger/ 76-car Folgefonn began life as a diesel-powered vessel, before undergoing an electrical system retrofit in 2014, arranged by the partners in NCE Maritime CleanTech. This retrofit saw Corvus Energy install its Energy Storage System (ESS) solution aboard Folgefonn, enabling the ferry to operate in either hybrid- or pure-electric mode.Corvus Energy also supplied the vessel with 221 batteries, rated 6.5kWh apiece, resulting in a combined capacity of 1MWh. Folgefonn was also equipped with a pair of Wärtsilä electric motors – one located at each end of the vessel, and each rated 750kW.

The arrangement of Wärtsilä’s wireless induction charging system involves two charging plates: one built into the side of the vessel, the other fixed on the quay, ready to provide year-round charging services to Folgefonn. Sørfonn adds: “The onboard charging plate is embedded flush with the substructure, and can be placed where it is convenient, or where you want to standardise the position.” Even at a distance of 500mm, the quayside plate can transfer full power, via the process of inductive power transfer, to the shipboard plate, and subsequently to the ferry’s battery pack. Designed as a modular unit, the quayside plate can be moved, if necessary, to other locations in the harbour or port. The quayside plate (and auxiliaries) measures 1,500mm x 800mm x 2,800mm and weighs approximately 2tonnes.

Following the successful completion of vessel charging tests conducted aboard Folgefonn, Sørfonn reveals that “up to 2.5MW of power can be transferred via a standard plate, but scaling is easier for larger transfer,” with charging times typically spanning five to 20 minutes – although a lower state of charge could necessitate a longer charging period. He adds: “As Folgefonn is a plug-in hybrid ferry, only parts of the energy will be transferred from shore.”

As well as sparing the operator the costs of cable/plug/component maintenance, the wireless induction charging solution can also, Sørfonn says, grant the operator “up to 20% more utilisation of the available charging time”. He continues: “The plug and cable depend on a mooring system to be safe, and also to interlock with the ramp. This takes at least one minute longer than making the connection via a wireless charger: therefore, for a five-minute-long charging period, eliminating one minute saves 20%.”

Passenger and crew safety were also prime considerations when developing the wireless induction charging solution. Sørfonn explains: “The system uses implemented logic to ensure a loss of power to any areas other than the charging plate, so there is no risk of parts of the vessel overheating. The magnetic fields created by the system are also low – far below EU standards – due to efficient shielding.”